Froth flotation beneficiating material containing dolomite or magnesite



Patented May 9, 1950 FROTH FLOTATION BENEFICIATING MATE- RIAL CONTAINING DOLOMITE OR MAGNE- SITE Thorbiorn Heilmann, Copenhagen, Denmark, assignor to Separation Process Company, Catasauqna, Pa., a corporation of Delaware No Drawing. Application February 25, 1947, Se-

{19116170. 730,756. In Denmark February 27,

11 Claims. (cl. 209-167) This invention relates to the beneflciation by froth flotation of ores relatively rich in calcite containing an undesirable proportion of magnesium carbonate in the form of magnesite (MgCOa) or dolomite (CaCO3.MgCO3). More particularly, the invention relates to the removal as a froth concentrate of magnesite or dolomite from calcite and siliceous materials, and, when further enrichment of the calcite is desired, includes the subsequent processing of the flotation residue to produce a higher grade calcite product with good weight recovery. The process of the invention is of particular importance in the pro duction of hydraulic and burnt lime, and in the treatment of cement raw materials to produce mixtures having reduced magnesium carbonate content which are suitable for use in the production of modern cements of predetermined compound compositions.

Various methods of beneflciating magnesite ores containing relatively minor proportions of calcite have heretofore been proposed and operated. These methods have involved the production of a magnesite of high purity by froth flotation using fatty acids and soaps thereof in the presence of such conditioning agents as sodium silicate, pyrophosphates, and acid salts. It has not been possible, however, by such methods to attain a satisfactory selectivity in cases where it has been desired to produce a high grade'calcite from a raw material relatively rich in calcite and containing also undesirable proportions of magnesite or dolomite. This may, in part, be due to the effect of slime coatings causing a loss in selectivity of collector reagents as between calcite and magnesite or dolomite. It is also true that no great selectivity can be attained between calcite and the other materials by the use of most commonly employed anionic collectors.

In the manufacture of Portland cement from many types of natural raw materials unsuitable for direct use, it is possible by a subtractive treatment to remove an undesired mineral or to so separate the various components that they may be recombined to give satisfactory raw material mixtures for burningin a kiln to produce the various present day types of Portland cement. Such treatments, including froth flotation as one method of separation, was originally proposed by Charles H. Breerwood in U. S. Patent No. 1,931,921. Since then, a number of further methods of treatment have been developed by him and others, some of which included froth flotation. Magnesia in quantities above a maximum limit is an undesirable component of a cement raw material mixture, because a negligible proportion enters intochemical combination during the burning process and a major part of such magnesia appears in the clinker in the form of periclase, a compound which causes delayed expansion and ultimate disentegration of concrete. Magnesia generally occurs in cement rock in the form of silicates, such as for example mica, and as carbonates, usually masnesite or dolomite, which is a double calcium magnesium carbonate. Methods of processing to reduce excessive magnesia content when present in the first mentioned form have proved suecessful in plant'practice, but no satisfactory method involving froth flotation has, to myknowledge, been proposed for a satisfactory reduction of the magnesia content when present in excessive amounts in the form of carbonates. In general, it may be said that, in spite of improved clinker quenching methods, cement rocks are not desirable as components of a cement raw material mix if they contain MgCOa in excess of about 4.5%. There are vast deposits of rock throughout the world containing substantial proportions of calcite which are now not suitable for use in cement making or for other purposes, such as the production of hydraulic or burnt lime, because of the fact that they contain a proportion of magnesite or dolomite in excess of this figure.

The present invention is accordingly directed to the provision of a froth flotation method whereby a high grade calcite product may be obtained from a material relatively rich in calcite but containing an undesirable proportion of magnesite or dolomite. The successful operation of my improved process depends on the removal of a fine fraction having a low micron particle size, and thereafter conditioning the material in an aqueous pulp having a pH value in excess of 8.5, to which has been added a soluble silicate such as sodium silicate, following which the magnesite or dolomite is froth floated by means of organic collector compounds containing acid groups, such as, for example, fatty acids or resin acids or mixtures thereof, or soaps of such reagents.

In many fiotation operations, it has been found essential to deslime the material prior to flotation. In the present invention, however, no such operation in the ordinary sense of the term is contemplated since a major proportion of the material after suitable grinding to cause the substantial release of the physical bonds between the minerals, is within the usually defined limits ofslimes. According to my process, a relatively small proportion by weight of material having a particle size in the low range of micron size, for example below microns, is removed by means of a physical separation process conducted in settling apparatus or centrifugal separators. The particle size split or weight percentage of finest particles removed, will vary according 'to the properties of the material being treated.

The collector reagents suitable for selectively floating the magnesite and the dolomite from the calcite in accordance with the invention may be any of the well known anionic types of organic acids now employed in the flotation of oxide ore minerals. Various higher fatty acids or mixtures thereof derived from animal and vegetable oils are in most cases available to the operator and.

give satisfactory results, I have also found that the alkali metal soaps of such acids or acid mixtures are effective. In many instances, a cheaper reagent may be desirable and in such cases a soap of waste oil" produced in the refining of animal and vegetable oils during the production of high grade fatty acids will prove satisfactory. Furthermore the soaps of resinous acids may be used with advantage either alone or in a mixture with other types of soap.

In the flotation of non-metallic minerals with anionic collectors, it has been observed that relatively strong alkaline pulps are undesirable since they tend to produce a barren overly soapy froth. In operating the process of my invention, however, I desire to produce in the pulp an alkalinity in excess of a pH value of 8.5 and preferably between about 9.0 and 11.0. This is in excess of any value normally attained by the addition of the usual conditioning or dispersing reagents of the alkaline type. According to the invention, such high pH regulation is effected by the addition to the pulp of a soluble alkaline material such as an oxide, hydroxide, or bicarbonate of an alkali or alkaline earth metal. Quick lime, hydrated lime, or other soluble alkalies, such as sodium hydroxide or potassium hydroxide, are examples of suitable materials. Other alkaline salts, sodium bicarbonate, ammonium bicarbonate, or calcium bicarbonates, a small proportion of which is normally present in hard water, may be used alone or more frequently in combination with oxides or hydroxides. For example, I have found that in some instances results have been considerably improved by the presence, in addition to a hydroxide, of a soluble bicarbonate in an amount greater than 0.1 gram per liter, which is considerably in excess of that normally present due to temporary hardness.

A further conditioning reagent in my proecss is a soluble silicate such as sodium silicate. Such a reagent has considerable advantage in the depression of the calcite and may be used in varying amounts depending on the material being treated. In most cases the amount required will be from 0.5 to 2.5 pounds per ton of dry materials. It may be added to the pulp in a conditioning step prior to the magnesium carbonate flotation or prior to the size classification to remove the finest calcite collectors. These will in general be organic acids such as fatty acids or resin acids or mixtures of the two, such for example as tall oil. Soaps of these acids or acid mixtures are also of great value in many instances.

In an alternative procedure in accordance with the invention, a method is provided which will be of particular advantage in beneficiating for the preparation of an ultimate cement raw material mixture, cement raw materials which contain both magnesium carbonate and siliceous materials in excess of that desired in the ultimate mixture. In accordance with the procedure the magnesite or dolomite are selectively removed by the above described treatment, and the tailing then treated with a cationic reagent to remove the undesired proportion of siliceous material. In the event that the siliceous portion of the raw material is composed of free silica (810:), and a silicate in the form of a mica, the mica may be selectively removed by means of a cationic reagent, preferably in the presence of a soluble iron or aluminum salt such as aluminum chloride, thus leaving as a flnal tailing the calcite and silica both of which will be required in the ultimate mixture fed to the kiln.

In the case of certain other materials containing appreciable amounts of silica or silicate minerals, it may be desirable to carry out the process of the invention by a slightly modifled procedure. The magnesite or dolomite and the calcite may, for example, be removed as combined concentrate by known anionic flotation treatment. The magnesium carbonate may then be separated from the calcite by further flotation in accordance with the above described procedure involving an increase in the pH value and the addition of the herein described reagents. In another modiflcation of the process of the invention, the treatment may consist in submitting the material to a cationic flotation in order to remove siliceous components and thereafter treating the tailing to separate the magnesium carbonate from the calcite in accordance with the described method.

The referred to reduction of the pH in the calcite residue may be accomplished by dewatering followed by dilution, or by the addition of a small amount of inorganic acid material, or by a combination of the two methods. The dewatering may be done in a centrifugal separator or a thickener and the alkaline water returned for further use in the flrst magnesia separation. The introduction of carbonic acid or sulphuric acid to the pulp, probably after at lease partial dewatering, will produce any desired degree of pH change. Preferably I reduce the pH value to a point within the range 7-8. In most cases good operating practice will indicate that a fairly efficient dewatering should be carried out followed by dilution with fresh water whereupon relatively small amounts of acid will be required to give the desired reduction in alkalinity.

It will be apparent to those skilled in the art that the raw materials to be treated must be crushed and ground to whatever degree is required to release effectively the mineral bonds between the various components. I have found that on a number of materials a wet grind so regulated as to produce a product which is approximately minus 150 mesh (Tyler) is suitable. In

1 other instances, of course, it will be found that other degrees of grinding are desirable.

The following examples will illustrate speciflc applications of the invention when applied to materials rich in calcite but containing proportions of magnesia in excess of that permissible in the preparation of a raw materials mix suitable for burning in a kiln to produce Portland cement.

Example I The raw material employed contained 73.2% calcite and 20.5% dolomite corresponding to a chemical analysis of 84.4% CaCO: and 9.3% M8003. The material was ground to approximately minus 150 mesh (Tyler) and subjected to a size classification in a. continuous centrifuge. The particle size of flne fraction removed was substantially all minus microns.

800 grams (dry weight) of the coarse centrifuge productwere subjected to froth flotation in a three liter laboratory cell and reagents, expressed in terms of pounds of reagent per ton of dry material feed, were added as follows:

sodium silicate 1.85 Quick lime 3.7

The hardness of the water list :1 was equal to 150 milligrams CaO per liter in the form of calcium bicarbonate. The pH of the pulp after reagent addition was 10.

As collecting and frothing reagents, a saponifled waste oil product and a resin acid soap were employed. The waste oil was produced in the refining of animal and vegetable oils during the production of high grade fatty acids. Two separate dolomite concentrates were removed in each case by the use of 0.25 lb. per ton of saponifled waste oil and 0.125 lb. per ton of resin soap. The following results were obtained.

The tailing from this operation is of sufliciently low magnesia content for use in a cement raw material mix,

In order to increase the efficiency of the overall operation a further treatment in accordance with one embodiment of the invention is desirable. The tailing from the just described operation was dewatered in a centrifugal separator to a moisture content of about 25% and then diluted with water. To this was added 0.25 lb. per ton (based on original flotation feed) of sulfuric acid which produced a pH in the pulp equal to 7.0. The pulp was returned to the flotation cell and 0.625 lb. per ton (based on flotation feed of the previous flotation) of a saponified tall oil were added. The weight of the calcite concentrate from this operation amounted to 62.7% of the original cell feed and analyzed 92.5% CaCOa and 4.0% MgCOa which corresponds to 87.7% calcite and 8.8% dolomite, a material suiilciently low in magnesia to be suitable for producing cement. The final tailing containing the undesired quartz and silicate minerals amounted to 4.5% by weight of the original flotation feed and analyzed 53.0% CaCOa and 5.9% MgCOs corresponding to 46.0% calcite and 12.9% dolomite.

Example II A further illustrative example of the method of the invention involves the production of a high grade calcite from a raw material containing 6 49.9% CaCO; and 37.5% MgCOa, the remainder being various silicate minerals. As in Example .I, the material was ground to about minus 150 mesh and treated in a centrifuge to remove the minus 10 micron fraction. A sample of the coarse fraction was treated in a flotation cell using the same reagents in the same, proportions as in Example I. The two froth concentrates, in this case containing magnesite, were combined and showed the following composition: 43.8% by weight on the cell feed analyzed 7.5% calcite and 81.2% magnesite. The tailing from this test was treated as in the previous example in order to improve the grade of the calcite. The calcite froth product amounted to 48.6% by weight 01' the original flotation feed and contained 88.8% calcite and 3.8% magnesite. The calcite flotation tailing was 7.6% by weight containing 5.3% calcite and 24.1% magnesite.

It is to be understood that the term calcite" as used herein applies generally to naturally occurring calcium carbonate as found, for example, in various types of cement rock, and does not apply to any particular crystalline form.

I claim:

1. A method for beneficiating by froth flotation a material containing calcium carbonate and a substantially less but an undesired high proportion of a magnesium carbonate mineral of the class consisting of magnesite and dolomite, which comprises separating from the material a'fraction containing a major portion of all the particles present therein having a size below about 10 microns, increasing the alkalinity of an aqueous pulp of the material above about 10 microns in size to a pH value in excess of 8.5 by the addition of at least one alkaline material selected from the class consisting of the oxides, hydroxides, and soluble bicarbonates of the alkali and alkaline earth metals, subjecting the alkalized pulp of said material in the presence of a soluble silicate to the action of at least one anionic collector for oxidized minerals selected from the class consisting of the higher fatty acids, resinous acids, and alkali metal soaps thereof, aerating the pulp, and removing the magnesium carbonate mineral as a froth concentrate.

2. A method for beneficiating by froth flotation a material containing calcium carbonate and a substantially less but an undesired high proportion of a magnesium carbonate mineral of the class consisting of magnesite and dolomite, which comprises separating from the material a fraction containing a major portion of all the particles present therein having a size below about 10 microns, increasing the alkalinity of an aqueous pulp of the material above about 10 microns in size to a pH value in excess of 8.5 by the addiing of the higher fatty acids, resinous acids, and

alkali metal soaps thereof, aerating the pulp, and removing the magnesium carbonate mineral as a froth concentrate.

3. A method for beneficiating by froth flotation a material containing calcium carbonate and a substantially less but an undesired high proporportion of all the particles present in said material having a size below about microns, subjecting the material above about 10 microns in size in the form of an aqueous pulp having a pH value in excess of 8.5 and in the presence of a soluble silicate to the action of at least one anionic collector for oxidized minerals selected from the class consisting of the higher fatty acids, resinous acids, and alkali metal soaps thereof, aerating the pulp, and removing the magnesium carbonate mineral as a froth concentrate.

4. A method for beneflciating by froth flotation a material containing calcium carbonate and a substantially less but an undesired high proportion of a magnesium carbonate mineral of the class consisting of magnesite and dolomite, which comprises separating from the material a fraction containing a major portion of all the particles present therein having a size below about 10 microns, increasing the alkalinity of an aqueous pulp of the material above about 10 microns in size to a pH value in excess of 8.5, and subjecting the alkalized pulp of said material in the presence of a soluble silicate, to the action of at least one soap of a high fatty acid, aerating the pulp, and removing the magnesium carbonate mineral as a froth concentrate.

5. A method for beneflciating by froth flotation a material containing calcium carbonate and a substantially less but an undesired high proportion of a magnesium carbonate mineral of the class consisting of magnesite and dolomite, which comprises separating from the material a fraction containing a major portion of all the particles present therein having a size below about 10 microns, increasing the alkalinity of an aqueous pulp of the material above about 10 microns in size to a pH value in excess of 8.5, and subjecting the alkalized pulp of said material in the presence of a soluble silicate, to the action of at least one resinous acid soap, aerating the pulp, and removing the magnesium carbonate mineral as a froth concentrate.

6. A method for beneflciating by froth flotation a material containing calcium carbonate and a substantially less but an undesired high proportion of a magnesium carbonate mineral of the class consisting of magnesite and dolomite, which comprises separating from the material a fraction containing a major portion of all the particles present therein having a size below about 10' microns, subjecting the material above about 10 microns in size in the form of an aqueous pulp having a pH value in excess of 8.5 and in the presence of a soluble silicate and a soluble bicarbonate in excess of 0.1 gram per liter to the action of at least one anionic collector for oxidized minerals selected from the class consisting of the higher fatty acids, resinous acids, and alkali metal soaps thereof, aerating the pulp, and.removing the magnesium carbonate mineral as a froth concentrate.

7. A method for beneflciating by froth flotation a material containing calcium carbonate and a substantially less but an undesired high proportion of a magnesium carbonate mineral of the class consisting of magnesite and dolomite, which comprises separating from the material a fraction containing a major portion of all,the particles present therein having a size below about 10 microns, subjecting the material above about 10 microns in size in the form of an aqueous pulp having a pH value in excess of 8.5 and in the presence of a soluble silicate to the action of at least one anionic collector for oxidized minerals lector.

8. A method for beneflciating by froth flotation a material containing calcium carbonate and a substantially less but anundesired high proportion of a magnesium carbonate mineral of the class cons sting of magnesite and dolomite, which comprises separating from the material a fraction containing a major portion of all the par ticles present therein having a size below about 10 microns, subjecting the material above about 10 microns in size in the form of an aqueous pulp having a pH value in excess of 8.5 and in the presence of a soluble silicate to the action of at least one anionic collector for oxidized minerals selected from the class consisting of the higher fatty acids, resinous acids, and alkali metal soaps thereof, aerating the pulp, removing themagnesium carbonate mineral as a froth concentrate, reducing the pH of the residual pulp to a value below 8.5 by replacing a substantial proportion of the alkaline water with fresh water and adding a mineral acid, and froth floating the calcite therefrom by means of an anionic calcite collector.

9. A method for beneflciating by froth flotation a material containing calcium carbonate and a substantially less but an undesired high proportion of a magnesium carbonate mineral of the class consisting of magnesite and dolomite, and containing at least one siliceous material in undesired excess, which comprises separating from the material a fraction containing a major portion of all the particles present therein having a size below about 10 microns, subjecting the material above about 10 microns in size in the form of an aqueous pulp having a pH value in excess of 8.5 and in the presence of a soluble silicate to the action of at least one anionic collector for oxidized m nerals selected from the class consisting of the higher fatty acids, resinous acids, and alkali metal soaps therof, aerating the pulp, removing the magnesium carbonate mineral as a froth concentrate, and separating from the residual enriched calcite pulp at least a part of the siliceous material contained therein by means of a cationic collector, having differential selective collecting capacity for siliceous minerals and calcite.

10. In a method of beneflclating, for the preparation of an ultimate cement raw material mixture, cement raw materials which contain calcium carbonate and magnesium carbonate in the form of a mineral of the class magnesite and dolomite, with the magnesium carbonate being present in amount substantially less than the calcium carbonate but in excess of that desired in the ultimate mixture, the improvement which comprises subjecting the raw material to a size classification to remove a major portion of all the particles of a size below about 10 microns, adjusting the alkalinity of an aqueous pulp of the material above about 10 microns in size to a value in excess of 8.5, and subjecting the alkalized pulp of said material in the presence of sodium silicate to a froth flotation operation in which the excess magnesium carbonate is removed as a concentrate by means of at least one anionic collector for oxidized minerals selected from the class consisting of the higher fatty acids, resinous acids, and soaps thereof. I

11. In a method of beneflciating, for the preparatlon of an ultimate raw material mixture, cement raw materials which contain calcium carbonate and magnesium carbonate in the form of a mineral of the class magnesite and dolomite, with the magnesium carbonate being present in amount substantially less than the calcium carbonate but in excess of that desired in the ultimate mixture, and including an amount of at least one siliceous mineral in excess of that desired in the ultimate mixture, the improvement which comprises subjecting the raw material to a size classification to remove a major portion of all the particles of a size below about 10 microns, adjusting the alkalinity of an aqueous pulp of the material above about 10 microns in size to a value in excess of 8.5, subjecting the alkalized pulp of said material in the presence of h pulp at least a part of the siliceous material co tained therein by means of a cationic collector having differential selective collecting capacity for siliceous minerals and calcite.

THORBJORN HEILMANN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,028,313 Breerwood Jan. 21, 1936 2,205,923 Doerner June 25, 1940 2,208,143 Weinig July 16, '1940 2,214,716 Breerwood Sept. 10, 1940 2,238,439 Bishop Apr. 15, 1941 2,255,139 Vogel-Jorgensen Sept. 9, 1941 2,363,104 Weinig Nov. 21, 1944 2,373,123 Lefforge A r. 10, 1945 OTHER REFERENCES Concentration of Low Grade Magnesite Ores by Flotation, State College of Washington Bull. p-l, pages 12, 13, 27.

Taggart, Handbook of Mineral Dressing, section 12, page 96. 

1. A METHOD FOR BENEFICIATING BY FROTH FLOTATION A MATERIAL CONTAINING CALCIUM CARBONATE AND A SUBSTANTIALLY LESS BUT AN UNDESIRED HIGH PROPORTION OF A MAGNESIUM CARBONATE MINERAL OF THE CLASS CONSISTING OF MAGNESITE AND DOLOMITE, WHICH COMPRISES SEPARATING FROM THE MATERIAL A FRACTION CONTAINING A MAJOR PORTION OF ALL THE PARTICLES PRESENT THEREIN HAVING A SIZE BELOW ABUT 10 MICRONS, INCREASING THE ALKALINITY OF AN AQUEOUS PULP OF THE MATERIAL ABOVE ABOUT 10 MICRONS IN SIZE A PH VALUE IN EXCESS OF 8.5 BY THE ADDITION OF AT LEAST ONE ALKALINE MATERIAL SELECTED FROM THE CLASS CONSISTING OF THE OXIDES, HYDROXIDES AND SOLUBLE BICARBONATES OF THE ALKALI AND ALKALINE EARTH METALS, SUBJECTING THE ALKALIZED PULP OF SAID MATERIAL IN THE PRESENCE OF A SOLUBLE SILICATE TO THE ACTION OF AT LEAST ONE ANIONIC COLLECTOR FOR OXIDIZED MINERALS SELECTED FROM THE CLASS CONSISTING OF THE HIGHER FATTY ACIDS, RESINOUS ACIDS, AND ALKALI METAL SOAPS THEREOF, AERATING THE PULP, AND REMOVING THE MAGNESIUM CARBONATE MINERAL AS A FROTH CONCENTRATE. 